This invention relates to an epoxy resin composition and a process for producing a semiconductor element having a seal coating of epoxy resin on a semiconductor material and being excellent in moisture resistance and thermal fatigue properties.
Conventional sealing processes for semiconductor elements can be divided into two groups: (1) a low-pressure transfer molding process using powdered epoxy compounds and (2) a potting process using two-component liquid epoxy resins curable with acid anhydrides or amines. The former is suitable for mass production of semiconductors such as diodes, transistors, LSI, etc., and the latter is suitable for the production of composite parts such as power module hybrid integrated circuits (IC), etc.
The epoxy compounds usable for the low-pressure transfer molding are usually those obtained by curing phenol-novolac type epoxy resins or cresol-novolac type epoxy resins with dicyandiamide or a phenol-novolac resin. In the potting process, epichlorhydrin-bisphenol type epoxy resins which are liquid at room temperature are usually cured by using acid anhydrides which are liquid at room temperature.
But there are many defects in these processes in that, in the case of semiconductor elements obtained by the transfer molding, adhesiveness between lead terminals and the resin is poor due to the presence of an internal mold release agent, moisture is easily penetrated from the interface and thus reliability is not sufficient, while in the case of the potting process, ester bonds present in the cured product are poor in moisture resistance.